The broad, long-term objective of this proposal is to develop low cost direct digital x-ray imaging systems for general application in radiology and radiation therapy. The Specific Aims are (1) to measure the imaging properties of an XLV (x-ray sensitive light valve) based on the use of a-Se (amorphous-selenium) and a TN (twisted nematic) and ECB (electrically controlled birefringence) liquid crystal cells and develop a theoretical model that can predict the behavior precisely, (2) to design and construct XLV optimized for specific imaging tasks, (3) to challenge the XLV technology to perform in a quantum limited manner for the three radiographic procedures (chest radiography, mammography, and portal imaging) by independent evaluation of XLV/scanner imaging prototypes. The health relatedness of the project is that it will provide a low cost system for any application in radiology and radiation therapy that will maintain or surpass currently available image quality, produce images quickly while doing so at greatly reduced cost, particularly the capital cost. The system has the potential to be manufactured locally in every country with sufficient infrastructure making this an empowering technology for developing countries as well as a cost effective solution for clinics in North America. The research design is that we will combine three well-established technologies, using a-Se as an x-ray to image charge transducer, liquid crystal display technology, and digital optical readout to achieve our goal. The concept is that the latent charge image created on the a-Se layer by interaction with x-rays is made into visible image by physically coupling it to a liquid crystal display. This visible image is then readout optically by a digital camera. The Methods to be used are linear systems analysis, Monte Carlo simulation, detective quantum efficiency (DQE) measurement, phantom tests, as well as comparison of performance with state of the art flat panel imagers.